1. Field of Invention
This disclosure relates to a pad driving circuit to drive a pad circuit of a input/output system.
2. Description of Related Art
The switching or transition time of an output signal, referred to as the slew rate, describes the rate at which the voltage of the output signal changes with respect to time (dv/dt). Ideally, the slew rate of the circuit would be infinitely high, causing the output signal to change from one logic state to the other logic state instantaneously. However, due to natural effects and energy storage of the components connected to the output pads of the IC, the logic state cannot change instantaneously. A great amount of time required for the output signal to transition from one logic state to the other logic state reduces the switching speed of the IC.
Modern ICs require high switching speeds. For example, ICs used in signal communication applications must comply with the applicable communication specifications and protocols. Many of these protocols, such as small computer standard interface (SCSI), the personal computer interface (PCI) bus interconnect standards, and the mobile driver IC, specify drive signal strength, signal delay time from input to output, and the slew rates of the output signal. It may be particularly difficult to meet these specifications under circumstances where the extent of the load which may be connected to the output pads of a communication IC varies substantially.
Therefore, there is a need for a new pad driving scheme which can improve the pad timing without enlarging the pad size.